1. Field of the Invention
The present invention relates to a matrix material for a carbon fiber-reinforced composite.
2. Description of the Related Art
A structure made of a carbon fiber-reinforced composite (CFRP) is lightweight and has excellent mechanical strength, and thus has been widely used in various fields. In general, the structure is produced using a CFRP prepreg in the following manner. A bundle (UD material) containing a plurality of carbon fibers, which are arranged parallel to each other, or a cross material containing carbon fibers woven horizontally and vertically is impregnated with a matrix material in order to form a prepreg sheet. A plurality of such prepreg sheets are stacked and molded under heat and pressure, and then the matrix material is hardened in order to obtain the CFRP structure. Preferably, the matrix material contains an epoxy resin as a resin component (matrix resin) from the viewpoints of strength and heat resistance, etc.
The prepreg and the structure prepared using the UD material exhibit lower strength in a direction perpendicular to the fiber direction than in the fiber direction. Furthermore, in the case that a plurality of prepreg sheets, which are prepared using the UD material or the cross material, are stacked, the resultant structure exhibits lower strength between the sheets in the stacking direction than in the fiber direction. Thus, the CFRP structure exhibits relatively low strength in a particular direction, and has an anisotropic strength property. However, in the case of using the structure as a member of an aircraft or the like, the structure is required to be extremely excellent in terms of strength, etc. Therefore, it is necessary to enhance the strength of the structure sufficiently in the particular direction.
The strength property of the entire structure, including the strength in the particular direction, can be improved by increasing interfacial adhesion between the carbon fiber and the matrix material, so as to suppress a reduction in strength due to anisotropy. Japanese Laid-Open Patent Publication Nos. 2011-214209 and 2006-249395 propose methods of this type.
The technology of Japanese Laid-Open Patent Publication No. 2011-214209 involves subjecting a carbon fiber bundle to a surface treatment. In such a treatment, a sizing agent of a mixture containing a first compound and a second compound at a particular ratio is applied to the surface of the carbon fiber bundle. More specifically, in such a treatment, the first and second compounds are dissolved in an organic solvent or water in order to prepare a sizing agent solution, the carbon fiber bundle is immersed in the solution, and the organic solvent and the like are evaporated and removed. The first compound has a hydroxyl group and/or a carboxyl group with a primary amino group and/or a secondary amino group, and the second compound has an epoxy group.
In Japanese Laid-Open Patent Publication No. 2006-249395, carbon fiber is surface-treated with a sizing agent containing a vinyl ester resin or the like, and an unsaturated matrix resin and an epoxy resin are mixed in order to prepare a matrix material. In the surface treatment, the surface of the carbon fiber is subjected to oxidation and then is impregnated with the sizing agent using an immersion roller, etc. The unsaturated matrix resin may be a vinyl ester resin or the like, and the epoxy resin may be a bisphenol A-type epoxy resin or the like.